The present invention relates to catalysts. In another aspect, the present invention relates to hydrocarbon cracking catalysts. In still another aspect, the invention relates to restoring the selectivity of hydrocarbon cracking catalysts. in yet another aspect, the invention relates to cracking a hydrocarbon feedstock.
Contaminants, for example, nickel, vanadium, and iron are found in significant concentrations in hydrocarbon feedstocks such as, for example, heavy oil fractions and in lower quality crude oils. These contaminants have a detrimental effect on the catalysts employed to convert these oils into gasoline and other valuable petroleum products, making processing of these oils economically unattractive. Unfortunately, because of limited supplies of oils containing low levels of contaminants, it is necessary to employ metals contaminated oils in hydrocarbon processes, such as catalytic cracking processes.
The contaminants found in feedstocks to cracking processes become deposited on the cracking catalyst. The deposition on the catalyst of, for example, nickel, vanadium and iron, causes a decrease in the activity of the cracking catalyst to convert the hydrocarbon feedstock into cracked products, including gasoline. The selectivity of the cracking catalyst for cracking the feedstock into gasoline as manifested by the portion of cracked products comprising gasoline is also decreased. The production of undesirable products, for example, hydrogen and methane, which must be compressed, necessitating additional equipment; and coke, which is deposited on the catalyst and must be burned off, requiring additional equipment and "off time", during which the catalyst is not employed for cracking, is significantly increased.
Because of these problems, the industry often replaces cracking catalysts contaminated by more than about 3,000 parts per million (ppm) of vanadium equivalents and iron. As used herein, the term vanadium equivalents is the measure of the combined parts by weight of vanadium and four times the nickel per million parts by weight of cracking catalyst including the weight of nickel, vanadium and iron on the cracking catalyst. There is thus a need for a cracking process suitable for use with contaminated feedstocks and contaminated cracking catalysts. There is also a need for a cracking catalyst which avoids at least some of the detrimental effects caused by deposits thereon of contaminants selected from nickel, vanadium and iron. There is also a need for a process of treating a contaminated cracking catalyst to increase its selectivity for producing gasoline boiling range type products.